According to the conventional practice, the concentration of a specific chemical composition, such as oxygen in a liquid or sulfur dioxide in a gas, is measured by the intensity of the fluorescent light emitted by the specific chemical composition. A probe kept in the fluid is irradiated by an excitation light source of a specific wavelength to emit fluorescent light of an intensity. The intensity of fluorescent light emitted by the probe is reduced at the time when the probe comes in contact with the specific chemical composition. This is due to the fact that the energy of the excited molecules on the probe is transmitted in a non-radiating manner to the molecules of the specific chemical composition. The energy is dissipated in the form of heat. The extent of reduction in intensity of the fluorescent light emitted by the probe is dependent on the concentration of the specific chemical composition such that the fluorescent light intensity is inversely proportional to the concentration of the specific chemical composition. As a result, the concentration of the specific chemical composition of the fluid can be calculated on the basis of the fluorescent light intensity of the probe. An alternative method makes no use of the probe. The fluid is irradiated by the excitation light source of a specific wavelength, thereby resulting in the fluorescent light emitted by the specific chemical composition. The intensity of the fluorescent light emitted by the specific chemical composition in a state of excitation is directly proportional to the concentration of the specific chemical composition. As a result, the concentration of a specific chemical composition can be calculated on the basis of the intensity of the fluorescent light emitted by the specific chemical composition.
Both methods described above have one thing in common that they make use of a grating or prism beam split to differentiate the excitation light and the fluorescent light. The spectral analysis of the fluorescent light is done by a spectrograph. The intensity of the fluorescent light is obtained on the basis of the data of the spectral analysis in conjunction with the integration circuit or the integration program. The concentration of the specific chemical composition is then compared and computed by the conversion equation. The concentration data are exhibited in a display.
Such conventional systems described above are capable of measuring the concentration of a specific chemical composition with precision; nevertheless they are not cost-effective in view of the complexity of the systems and the high cost of the spectrograph. The U.S. Pat. Nos. 5,973,330 and 5,738,997 disclose the similar technological applications in which the photosensor is used to receive the signal of fluorescent light. In addition, these two disclosures are also not cost-effective in view of the fact that they make use of the optical lenses, such as beam splitter, reflector, etc. to differentiate the excitation light and the fluorescent light which is brought about by the excitation light.